Chart Navigation & Plotting · Piloting — Luminous Range
On a clear night the geographic range of a light is 18 nm and its luminous range is 12 nm. At what distance can you expect to first see the light?
- A18 nautical miles — the geographic range always governs
- B12 nautical miles — the lesser of the two ranges governs✓ Correct
- C30 nautical miles — the ranges add
- D15 nautical miles — the average of the two
Explanation
You will see the light at the lesser of its luminous range (limited by intensity and visibility) and its geographic range (limited by Earth's curvature). Here luminous range of 12 nm is the limiting factor.
Authority: Bowditch (Pub. No. 9); NGA Light List, luminous and geographic range
Practice the full Chart Navigation & Plotting bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Chart Navigation & Plotting questions
- Chart Basics
On a Mercator chart, one nautical mile is measured using the:
- Chart Basics
The principal advantage of the Mercator projection for navigation is that:
- Chart Basics
Charted depths (soundings) on a U.S. chart are referenced to which tidal datum?
- Chart Basics
Vertical clearances of bridges and overhead cables on a U.S. chart are normally referenced to:
- Distance, Speed & Time
A vessel makes good 12 knots. How far does it travel in 20 minutes?
- Distance, Speed & Time
A vessel covers 9 nautical miles in 45 minutes. What is its speed?